Antenna reflector



' Jul 22, 1952 H, CLARK 2,604,595

ANTENNA REFLECTOR Filed Sept. 25, 1945 INVENTOR. TREVOR H. CZ HRKATTORNEY Patented July 22, 1952 oNiTEostares PATENT orrics "f 72,604,595 I ANTENNA REFLECTOR Trevor 'H. ClarkfBoonton, N. J., assignorto Federal -Telephone' and Radio Corporation,

New York, N. Y., a corporation of Delaware Application September 25,1945, Serial No.618 ,53 1

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This inventionfrelates to radiant energy antenna reflectors andmore'particularly to reflectors for use with directional antenna arrangements in a certain frequency range.

When a directionally sensitive radiation characteristic is desired in anantenna system it is generally necessary to provide one or morereflectors in conjunction with a given antenna. In order for thereflector to be efflcient, that is to operate with a high reflectioncoefficient, the reflector should be. designed to. possess highconductivity and for a given frequency should have dimensions such thatit is resonant in the onehalf wavelength mode. This characteristic isacceptable when very high frequencies are used. However, if a wide bandcharacteristic is required of-the reflector it should'be of suflicientsize as to be substantially non-resonant throughout the operating range.As the wavelength increases, the physical dimensions of the reflectormore and more approach a length corresponding to one-half wavelengthuntil'one of the portions of the reflector corresponding to thepolarization of the radiation becomes resonant with a respectivewavelength. This causes the production of standing Waves along theseresonant portions of the reflector with a consequent increase in theback radiation of the reflector. When a radiation characteristicsensitive in only one direction is desired, an increase in backradiation, that is, sensitivity on both sides of the reflector is acause for ambiguity of indications.

It is accordingly an object of this invention to reduce back radiationsensitivity of an antenna reflector for comparatively low frequencies ina given band.

It is another object to reduce the formation of standing waves alongresonantly dimensioned portions of the reflector.

It is another object to provide a reflector which is non-resonant in anyone of its portions with respect to the lowest frequency in a givenband.

A still further object is to provide a reflector which may be madenon-resonant for vertically polarized or for horizontally polarizedradiation.

Still another object is to provide a reflector which is non-resonant inany of its portions over a wide band of frequencies.

In accordance with certain features of the invention, I provide areflector comprised of a rectangular metallic sheet in conjunction witha given antenna the horizontal and/or vertical edges of which approachor may be less than the one-half wavelength for a given low frequency ofthe band dealt with. In order to avoid 2 Claims. -(Cl. 250-33135) .1 2the formation of standing waves I provide conductive extensions of theedges of the reflector which correspond to the respective polarizationof the radiation to which the antenna is exposed. In accordance withanother feature of the invention I provide extensions for the edges aswell as for intermediate portions of the reflector parallel to the edgeswhereby the reflector is effective in avoiding the formation of standingwaves on any part of its surface which may be resonant over a broad bandof frequencies. with still another feature of this invention I providean eifective extension of therespective edges of the reflector Withoutactually having to introduce a physical extension thereo These and otherfeatures and objects of'the invention will become more apparent upontheconsideration of the following detailed description of embodiments to beread in connection with the accompanying drawings in which:

Fig. 1 represents a plan view of a reflector in' accordance with myinvention designed'for' horizontally polarized radiation;

Fig. 2 represents a reflector constructed in accordance with theinvention for vertically polarized radiation;

Figs. 3 and 4 are variations of a reflector designed for a widefrequency band; and

Fig. 5 is a plan view of a reflector, certain edges of which have beenlengthened in another way.

Referring to the drawings, the reflector of Fig. 1 comprises arectangular metallic sheet I having a horizontal dimension given by oneof the horizontal edges 2 and a vertical dimension which is given by oneof its vertical edges 3. The horizontal edges have been provided withhorizontal extension bars 4, 5, 6 and 1 which extend the horizontaldimensions to some value In. A dipole antenna 8 designed for operationover a relatively'wide band of frequencies is suitably mounted in frontof the reflecting surface I. The antenna is a horizontal dipole,particularly sensitive to waves of a horizontal polarization. At thelower frequencies of the wave band the horizontal reflector dimensionmay be a half wavelength or less. The extensions added thereto are suchthat In is greater than a half wavelength at the operative frequenciesso that resonance effects to horizontal polarized energy will besubstantially eliminated.

In Fig. 2 the reflecting surface I has been provided with verticalextensions 9, H), II and I2 of its vertical edges 3. These extensionsare such that Iv is greater than a half Wavelength so that verticalpolarized resonance effects will In accordance 3 be substantiallyreduced or eliminated. It should be clear that if the antenna isdesigned to operate at both horizontal and vertical polarization, twosets of extensions such as shown in Figs. 1 and 2, may be used on thesame reflector.

The reflector of Fig. 3, which is intended to operate over a wide band,instead of having individual bar-like extensions of its edges, has beenprovided with wing-like extensions I3, l4, l and I6, which have theirmaximum dimension in line with the edges 2 and are reduced to zero inline with the intermediate horizontal portionsof the reflector. Thisconstruction will serve further to reduce resonance effects which mightoccur intermediate the edges of the reflector.

In Fig. 4 a reflector is shown provided with extensions similar ineffect to those of Fig..3. However, instead of continuous extensionsurfaces, individual bars as at I! and I3 are attached to oppositelydisposed edges of reflector l parallel to the plane of polarization. Thebars I! and l8 progressively assume a smaller size from the outerportions of said edges toward the center portions of said edges of thereflector.

Another system for obtaining an eflective extension of the resonantedges of a reflector has been suggested in Fig. 5 where the horizontaledges have been increased in length by being serrated as at I9 and 20.

While I have shown a few examples of how resonance may be avoided in areflector for individual and wide band frequencies, it is to be notedthat resonance may be eliminated in other ways analogous to the above. 1

While I have described above the principles of my invention inconnection withspecific apparatus, it is to be clearly understood thatthis description-is made only. by way of example and not as a limitationon the scope of my invention as defined in the objects and theaccompanyin laims.

;I claimr 1. 'A reflector for use with an antenna adapted to operate ona given band of frequencies and with a predetermined polarization,comprising a member having a plane reflecting surface and a plurality ofconductive bar-like extension elements extending from opposite edges ofsaid member in the same plane as said reflecting surface and parallel tothe plane of polarization, said elements having divers lengths andspacedly mounted from each other along the opposite edges of saidmember, whereby said reflector is rendered substantially aperiodic atthe operating frequencies in said band.

2. A reflector as claimed in claim 1, wherein said member comprises anelement having oppositely disposed edges, each edge having a centralportion and outer portions, said extension elements extending from bothsaid edges, the longest of said extension elements attached adjacent theouter portions of said edges and the shortest of said extension elementsattached adjacent the central portions of said edges, said extensionelements of intermediate lengths being disposed in ascending order fromthe central portions of said edges in accordance with their length.

TREVOR H. CLARK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Masters Aug. 30, 1949

